1. Field of the Invention
My present invention relates to indicating instruments, and more particularly to indicating instruments of the moving magnet type wherein a magnet is mounted on a shaft carrying a pointer one end of which is closely juxtaposed to a dial, and wherein an environing magnetic field is provided in the space provided by the shaft-mounted magnet and the direction of that magnetic field is varied in accordance with the momentary magnitude of a parameter whose magnitude is to be indicated on the dial by the pointer.
The present invention also relates to an apparatus for preventing the unwanted migration of fluid out of a chamber, including a chamber used to hold damping fluid in an indicating instrument, such as a moving-magnet or Bourdon-tube indicating instrument.
2. Description of the Prior Art
Moving magnet indicating instruments are well known in the prior art.
For example, a moving magnet indicating instrument of the cross-coil type is shown and described in U.S. Pat. No. 5,095,266, which was issued to Yukio Ohike and Tomohiro Sugiyama on Mar. 10, 1992. In the indicating instrument of this patent the magnetic field which environs the moving magnet is provided by electrical currents flowing through a pair of mutually perpendicular coils, said currents varying from moment to moment in accordance with the momentary magnitude of the quantity to be indicated.
Another moving magnetic indicating instrument of the cross-coil type is shown and described in U.S. Pat. No. 4,906,919, which was issued to Koichi Sato, Tatsuro Togawa and Toshiyuki Ohtake on Mar. 6, 1990.
Another type of moving magnet indicating instrument known in the prior art is typified by the differential pressure and flow instruments made and sold by Orange Research, Inc., of 140 Cascade Boulevard, Milford, Conn. 06460. In these instruments the magnetic field which environs the moving magnet, and which moves the pointer shaft and its associated dial pointer, is a permanent magnet which is moved with respect to the dial operating magnet by the fluid pressure or fluid flow the magnitude of which is to be indicated.
As is well known to those having ordinary skill in the moving magnet indicating instrument art, the moving magnet assemblies of such instruments, principally comprising the moving magnet, the shaft, and the dial pointer thereof, are characterized by low inertia and low friction, necessitating the provision of damping means. Further, due to the highly competitive economics of manufacturing and marketing of these instruments, such damping means must be as inexpensive and simple to assemble as possible. This requirement as led to the widespread adoption for this purpose of a small quantity of suitable damping fluid, such as silicone oil, disposed in the cavity formed by the housing of the instrument, containing the moving magnet, with no containment means to positively maintain the damping fluid within the housing.
Unfortunately, as is well known to those having ordinary skill in the art, there is a definite tendency for the damping fluid to migrate, via the clearance between the dial shaft and the surrounding portion of the instrument housing, to parts of the instrument where its presence is undesirable, such as the pointer, the dial face, and the lens of the instrument. Indeed, this is a problem with all indicating instruments that use damping fluids, including mechanical indicating instruments such as Bourdon tube indicating instruments.
Additionally, many of the prior art moving magnet indicating instruments are provided with pointer shafts which are of very small diameter, as compared with their overall length.
While the use of such small diameter pointer shafts saves weight and cost, it results in certain disadvantages, such as the inadvertent binding of the shaft, and the lack of sufficient contact surface area between the shaft and the wall of the central hole in the moving magnet, into which the shaft is press-fitted. Further, the small diameter of the pointer shaft severely limits the area of the shoulder turned therein which is used as part of the thrust bearing which prevents movement of the shaft into and out of the opening in the housing in which its pointer-bearing end is journaled.
It is believed that the documents listed immediately below contain information which is or might be considered to be material to the examination of this patent application.
U.S. Pat. Nos. 3,494,203, 3,778,711, 4,402,335, 4,492,920, 4,724,601, 5,017,862, 5,038,099
The term "prior art" as used herein or in any statement made by or on behalf of applicant means only that any document or thing referred to as prior art bears, directly or inferentially, a date which is earlier than the effective filing date hereof.
No representation or admission is made that any of the above-listed or cited documents is part of the prior art, or that a search has been made, or that no more pertinent information exists.
A copy of each of the above-listed or cited documents is being supplied to the United States Patent and Trademark Office herewith.